Or alternatively:
* Create a "sudoers" group at install time.
* Have the "%sudoers" in /etc/sudoers by default.

Just a small note: there's a "wheel" group, which has entries
in /etc/sudoers by default, but commented. This group is usually
for the administration users AFAIK, so it could be used instead of
"sudoers" group.
Cheers,
Caio Marcelo